1. Field of the Invention
The present invention relates to a lubrication monitoring device and method as well as to a rolling bearing assembly.
2. Description of the Related Art
The rolling bearing assembly for supporting a rotary shaft or the like is lubricated by a proper method in order to prevent seizing. The known lubrication method may be exemplified by a seal system wherein grease or solid lubricant is sealed in space between inner and outer rings of the rolling bearing assembly for lubrication, an oil bath system wherein the rolling bearing is operated as dipped in a lubricant, or the like. Unfortunately, these methods require a large quantity of lubricant which results in substantial lubricant waste.
On the other hand, there are also known a method wherein the lubricant is injected to a lubrication point by operating a pump, and a method which employs an oil-air lubrication system for feeding oil little by little. These methods have advantages of being capable of feeding the oil on an as-needed basis and wasting less lubricant. More recently, a so-called nanolubrication has been adopted wherein a rolling bearing is lubricated with oil droplets at a rate ranging from several nl/min to several hundred nl/min.
Japanese Unexamined Patent Publication No. 2007-92886 discloses a rolling bearing assembly which employs a micro pump for feeding the lubricant to space between the inner ring and the outer ring of the rolling bearing. The micro pump is adapted to draw the lubricant from a tank by means of a diaphragm pulsated by a piezoelectric device and to discharge a microscopic droplet of lubricant from a discharge nozzle at a predetermined time interval.
In the so-called nanolubrication, however, an absolutely small amount of lubricant is supplied as described above. Hence, the nanolubrication is prone to entail poor lubrication unless the lubricant continues to be fed at the predetermined time intervals. It is therefore crucial to monitor the condition of feeding the oil droplet and to determine whether the lubricant is fed properly or not.